The invention relates to a process for false-twist spinning in which the fiber material first travels through a drafting unit, then through at least one false-twisting nozzle and subsequently through a withdrawal device. The false-twist distribution in the yarn between the false-twisting nozzle and the drafting unit is influenced such that the false twist in the inlet area of the false-twisting nozzle is larger than in the outlet area of the drafting unit. The invention also relates to an arrangement for performing this false-twist spinning process.
In a process and an arrangement of the initially mentioned type described in German Patent Document DE-A 36 31 400, devices are arranged between the drafting unit and the following false-twisting nozzle, by which a twisting brake is created by means of which the false twist is weakened which extends back in the yarn from the false-twisting nozzle to the drafting unit. In some embodiments, the guiding elements, which are driven to perform rotations around an axis transversely to the travelling direction of the yarn, form a deflection having a guiding surface moving in the travelling direction of the yarn. By this measure, the spreading-away of the edge fibers or fiber ends is to be facilitated and made more uniform.
It is also known from German Patent Document DE-A 37 14 212 to arrange between the drafting unit and the false twisting nozzle a rotating guiding element to which devices are assigned for changing the travelling direction of the yarn transversely to the direction of the movement of the rotating guiding element. As a result, the fiber structure is to be loosened so that the sliver widens in the transverse direction before it enters into the air nozzle.
It is also known from European Patent Document EP-B 0 057 876 to provide a deflecting roller between a drafting unit and a false-twisting nozzle which has the purpose of deflecting the sliver in such a manner that, as a result of generated centrifugal forces, fibers are spread away which subsequently are to wind around the yarn core.
It is also known from European Patent Document EP-B 0 085 017 to connect a compressing roller in the form of a roller provided with a flute behind a drafting unit, the groove base of which is subjected to suction. As a result, the sliver is to be compressed. This compressing roller is to have the effect that the twist provided to the yarn by the spinning element which follows is limited completely to the area between the twisting element and the compressing roller so that the area between the drafting unit and the compressing roller remains completely untwisted. The untwisted condition of the sliver in the area between the delivery rollers of the drafting unit and the compressing roller has the purpose of making it possible that, as a result of the compressing roller, a positive and a negative draft can be obtained and the delivery roller can be driven at a speed which corresponds to the delivery speed or differs from it.
It is also known from European Patent Document EP-A 0 305 971 to connect behind a drafting unit a pair of disks which rotate in opposite directions and which have a nip area and an annular sieve area subjected to suction.
It is also known from German Patent Document DE-C 24 16 880 to provide transfer conveyor belts between a pair of delivery rollers of a drafting unit and false-twisting nozzles which follow, which transfer conveyor belts wind around the rollers of the pair of delivery rollers and open up in the travelling direction of the yarn.
It is also known from German Patent Document DE-C 33 10 285 to provide a sliding surface, which moves transversely with respect to the yarn travelling direction, between the delivery rollers of a drafting unit and a turning-in device for the fiber roving, this sliding surface having the purpose of bending projecting fiber ends transversely with respect to the yarn axis.
It is an object of the invention to provide a process of the initially mentioned type by which the yarn quality is improved.
This object is achieved according to the invention by accelerating the edge fibers of the yarn in the area between the drafting unit and the inlet area of the false twisting nozzle in the travelling direction of the yarn to a higher speed than the core of the yarn.
In this development according to the invention, in addition to the influencing of the false-twist distribution, according to which a greater false twist is obtained in the inlet area of the false-twisting nozzles than in the outlet area of the drafting unit, it is also provided that edge fibers or fiber ends are detached and, in comparison to the core of the yarn having a lower speed, are accelerated in the direction toward the false-twisting nozzle. As a result, on the one hand, the number of the detached fiber ends which later wind around the yarn is increased and made more uniform while, on the other hand, the slope of the windings becomes steeper than had been previously possible. As a result, a yarn or a thread is produced which has a more uniform structure, and the tearing strength of which is increased by approximately 30% in comparison to comparable yarns or threads.
In a further development of the invention, it is provided that the edge fibers are accelerated to a speed which amounts to approximately 1.3 times to 1.8 times the speed of the core of the yarn. It was found that below this range, the endeavored effect, particularly the increase of the tearing strength, does not occur or occurs to a not yet very high degree, whereas above this range the endeavored effect decreases again.
In a further development of the invention, in an arrangement for false-twist spinning having a drafting unit, at least one false-twisting nozzle and a withdrawal device as well as a guiding element which is arranged between the drafting unit and the air nozzle, is driven to perform rotations around an axis disposed transversely with respect to the yarn travelling direction, and forms a deflection with a yarn guiding surface moving in the travelling direction of the yarn, it is provided that the guiding surface is driven at a speed which is higher than the delivery speed of the drafting unit and higher than the withdrawal speed of the withdrawal device.
In this arrangement, the yarn rolls along transversely to its travelling direction on the guiding surface so that a weakening of the false twist occurs originating from the false-twisting nozzle in the direction toward the pair of delivery rollers of the drafting unit as a result of the provided false twist. In this case, only the edge fibers or fiber ends are taken along by the guiding surface so that they are spread away from the yarn core and aligned. As a result, the number of the spread-away fiber ends which are later wound around the yarn is increased and made uniform. In addition, the slope of the winding clearly becomes steeper. As a result of the rolling on the moving guiding surface, it is also achieved that the yarn, as a whole, has a rounder cross-section than previously. There are practically no areas where there is no winding-around of fiber ends.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.